From 5af6807bdb10d1af9d412d7d6c177ba8440adffb Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Wed, 5 Jul 2023 20:34:45 -0700 Subject: [PATCH] bpf: Introduce bpf_mem_free_rcu() similar to kfree_rcu(). Introduce bpf_mem_[cache_]free_rcu() similar to kfree_rcu(). Unlike bpf_mem_[cache_]free() that links objects for immediate reuse into per-cpu free list the _rcu() flavor waits for RCU grace period and then moves objects into free_by_rcu_ttrace list where they are waiting for RCU task trace grace period to be freed into slab. The life cycle of objects: alloc: dequeue free_llist free: enqeueu free_llist free_rcu: enqueue free_by_rcu -> waiting_for_gp free_llist above high watermark -> free_by_rcu_ttrace after RCU GP waiting_for_gp -> free_by_rcu_ttrace free_by_rcu_ttrace -> waiting_for_gp_ttrace -> slab Signed-off-by: Alexei Starovoitov Signed-off-by: Daniel Borkmann Acked-by: Hou Tao Link: https://lore.kernel.org/bpf/20230706033447.54696-13-alexei.starovoitov@gmail.com --- include/linux/bpf_mem_alloc.h | 2 + kernel/bpf/memalloc.c | 129 +++++++++++++++++++++++++++++++++++++++++- 2 files changed, 128 insertions(+), 3 deletions(-) diff --git a/include/linux/bpf_mem_alloc.h b/include/linux/bpf_mem_alloc.h index 3929be5..d644bbb 100644 --- a/include/linux/bpf_mem_alloc.h +++ b/include/linux/bpf_mem_alloc.h @@ -27,10 +27,12 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma); /* kmalloc/kfree equivalent: */ void *bpf_mem_alloc(struct bpf_mem_alloc *ma, size_t size); void bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr); +void bpf_mem_free_rcu(struct bpf_mem_alloc *ma, void *ptr); /* kmem_cache_alloc/free equivalent: */ void *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma); void bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr); +void bpf_mem_cache_free_rcu(struct bpf_mem_alloc *ma, void *ptr); void bpf_mem_cache_raw_free(void *ptr); void *bpf_mem_cache_alloc_flags(struct bpf_mem_alloc *ma, gfp_t flags); diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c index e5a87f6..17ef2e9 100644 --- a/kernel/bpf/memalloc.c +++ b/kernel/bpf/memalloc.c @@ -101,6 +101,15 @@ struct bpf_mem_cache { bool draining; struct bpf_mem_cache *tgt; + /* list of objects to be freed after RCU GP */ + struct llist_head free_by_rcu; + struct llist_node *free_by_rcu_tail; + struct llist_head waiting_for_gp; + struct llist_node *waiting_for_gp_tail; + struct rcu_head rcu; + atomic_t call_rcu_in_progress; + struct llist_head free_llist_extra_rcu; + /* list of objects to be freed after RCU tasks trace GP */ struct llist_head free_by_rcu_ttrace; struct llist_head waiting_for_gp_ttrace; @@ -346,6 +355,69 @@ static void free_bulk(struct bpf_mem_cache *c) do_call_rcu_ttrace(tgt); } +static void __free_by_rcu(struct rcu_head *head) +{ + struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu); + struct bpf_mem_cache *tgt = c->tgt; + struct llist_node *llnode; + + llnode = llist_del_all(&c->waiting_for_gp); + if (!llnode) + goto out; + + llist_add_batch(llnode, c->waiting_for_gp_tail, &tgt->free_by_rcu_ttrace); + + /* Objects went through regular RCU GP. Send them to RCU tasks trace */ + do_call_rcu_ttrace(tgt); +out: + atomic_set(&c->call_rcu_in_progress, 0); +} + +static void check_free_by_rcu(struct bpf_mem_cache *c) +{ + struct llist_node *llnode, *t; + unsigned long flags; + + /* drain free_llist_extra_rcu */ + if (unlikely(!llist_empty(&c->free_llist_extra_rcu))) { + inc_active(c, &flags); + llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra_rcu)) + if (__llist_add(llnode, &c->free_by_rcu)) + c->free_by_rcu_tail = llnode; + dec_active(c, flags); + } + + if (llist_empty(&c->free_by_rcu)) + return; + + if (atomic_xchg(&c->call_rcu_in_progress, 1)) { + /* + * Instead of kmalloc-ing new rcu_head and triggering 10k + * call_rcu() to hit rcutree.qhimark and force RCU to notice + * the overload just ask RCU to hurry up. There could be many + * objects in free_by_rcu list. + * This hint reduces memory consumption for an artificial + * benchmark from 2 Gbyte to 150 Mbyte. + */ + rcu_request_urgent_qs_task(current); + return; + } + + WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp)); + + inc_active(c, &flags); + WRITE_ONCE(c->waiting_for_gp.first, __llist_del_all(&c->free_by_rcu)); + c->waiting_for_gp_tail = c->free_by_rcu_tail; + dec_active(c, flags); + + if (unlikely(READ_ONCE(c->draining))) { + free_all(llist_del_all(&c->waiting_for_gp), !!c->percpu_size); + atomic_set(&c->call_rcu_in_progress, 0); + } else { + call_rcu_hurry(&c->rcu, __free_by_rcu); + } +} + static void bpf_mem_refill(struct irq_work *work) { struct bpf_mem_cache *c = container_of(work, struct bpf_mem_cache, refill_work); @@ -360,6 +432,8 @@ static void bpf_mem_refill(struct irq_work *work) alloc_bulk(c, c->batch, NUMA_NO_NODE); else if (cnt > c->high_watermark) free_bulk(c); + + check_free_by_rcu(c); } static void notrace irq_work_raise(struct bpf_mem_cache *c) @@ -488,6 +562,9 @@ static void drain_mem_cache(struct bpf_mem_cache *c) free_all(llist_del_all(&c->waiting_for_gp_ttrace), percpu); free_all(__llist_del_all(&c->free_llist), percpu); free_all(__llist_del_all(&c->free_llist_extra), percpu); + free_all(__llist_del_all(&c->free_by_rcu), percpu); + free_all(__llist_del_all(&c->free_llist_extra_rcu), percpu); + free_all(llist_del_all(&c->waiting_for_gp), percpu); } static void free_mem_alloc_no_barrier(struct bpf_mem_alloc *ma) @@ -500,8 +577,8 @@ static void free_mem_alloc_no_barrier(struct bpf_mem_alloc *ma) static void free_mem_alloc(struct bpf_mem_alloc *ma) { - /* waiting_for_gp_ttrace lists was drained, but __free_rcu might - * still execute. Wait for it now before we freeing percpu caches. + /* waiting_for_gp[_ttrace] lists were drained, but RCU callbacks + * might still execute. Wait for them. * * rcu_barrier_tasks_trace() doesn't imply synchronize_rcu_tasks_trace(), * but rcu_barrier_tasks_trace() and rcu_barrier() below are only used @@ -510,7 +587,8 @@ static void free_mem_alloc(struct bpf_mem_alloc *ma) * rcu_trace_implies_rcu_gp(), it will be OK to skip rcu_barrier() by * using rcu_trace_implies_rcu_gp() as well. */ - rcu_barrier_tasks_trace(); + rcu_barrier(); /* wait for __free_by_rcu */ + rcu_barrier_tasks_trace(); /* wait for __free_rcu */ if (!rcu_trace_implies_rcu_gp()) rcu_barrier(); free_mem_alloc_no_barrier(ma); @@ -563,6 +641,7 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma) irq_work_sync(&c->refill_work); drain_mem_cache(c); rcu_in_progress += atomic_read(&c->call_rcu_ttrace_in_progress); + rcu_in_progress += atomic_read(&c->call_rcu_in_progress); } /* objcg is the same across cpus */ if (c->objcg) @@ -579,6 +658,7 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma) irq_work_sync(&c->refill_work); drain_mem_cache(c); rcu_in_progress += atomic_read(&c->call_rcu_ttrace_in_progress); + rcu_in_progress += atomic_read(&c->call_rcu_in_progress); } } if (c->objcg) @@ -663,6 +743,27 @@ static void notrace unit_free(struct bpf_mem_cache *c, void *ptr) irq_work_raise(c); } +static void notrace unit_free_rcu(struct bpf_mem_cache *c, void *ptr) +{ + struct llist_node *llnode = ptr - LLIST_NODE_SZ; + unsigned long flags; + + c->tgt = *(struct bpf_mem_cache **)llnode; + + local_irq_save(flags); + if (local_inc_return(&c->active) == 1) { + if (__llist_add(llnode, &c->free_by_rcu)) + c->free_by_rcu_tail = llnode; + } else { + llist_add(llnode, &c->free_llist_extra_rcu); + } + local_dec(&c->active); + local_irq_restore(flags); + + if (!atomic_read(&c->call_rcu_in_progress)) + irq_work_raise(c); +} + /* Called from BPF program or from sys_bpf syscall. * In both cases migration is disabled. */ @@ -696,6 +797,20 @@ void notrace bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr) unit_free(this_cpu_ptr(ma->caches)->cache + idx, ptr); } +void notrace bpf_mem_free_rcu(struct bpf_mem_alloc *ma, void *ptr) +{ + int idx; + + if (!ptr) + return; + + idx = bpf_mem_cache_idx(ksize(ptr - LLIST_NODE_SZ)); + if (idx < 0) + return; + + unit_free_rcu(this_cpu_ptr(ma->caches)->cache + idx, ptr); +} + void notrace *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma) { void *ret; @@ -712,6 +827,14 @@ void notrace bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr) unit_free(this_cpu_ptr(ma->cache), ptr); } +void notrace bpf_mem_cache_free_rcu(struct bpf_mem_alloc *ma, void *ptr) +{ + if (!ptr) + return; + + unit_free_rcu(this_cpu_ptr(ma->cache), ptr); +} + /* Directly does a kfree() without putting 'ptr' back to the free_llist * for reuse and without waiting for a rcu_tasks_trace gp. * The caller must first go through the rcu_tasks_trace gp for 'ptr' -- 2.7.4